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Issue 4, 2009
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Rate constants and the H atom branching ratio of the reactions of the methylidyne CH(X2Π) radical with C2H2, C2H4, C3H4 (methylacetylene and allene), C3H6 (propene) and C4H8 (trans-butene)

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Abstract

The reactions of the CH radical with several unsaturated hydrocarbons C2H2 (acetylene), C2H4 (ethylene), C3H4 (methyl-acetylene and allene), C3H6 (propene) and C4H8 (trans-butene) were studied at room temperature, in a low-pressure fast-flow reactor. CH(X2Π, v = 0) radicals were obtained from the reaction of CHBr3 with potassium atoms. The overall rate constants at 300 K are CH + C2H2: (3.6 ± 0.6) × 10−10, CH + C2H4: (3.1 ± 0.6) × 10−10, CH + C3H4 (methyl-acetylene): (3.4 ± 0.6) × 10−10, CH + C3H4 (allene): (3.6 ± 0.6) × 10−10, CH + C3H6 (propene): (4.2 ± 0.8) × 10−10 and CH + C4H8 (trans-butene): (4.0 ± 0.80) × 10−10 cm3 molecule−1 s−1 (errors are cited at the level of ±1σ). Absolute atomic hydrogen production was determined by vacuum ultra-violet (VUV) resonance fluorescence, H production from the CH + CH4 reaction being used as a reference. Observed H branching ratios for these CH reactions were: C2H2: 0.90 ± 0.08, C2H4: 0.94 ± 0.08, C3H4 (methyl-acetylene): 0.98 ± 0.08, C3H4 (allene): 0.97 ± 0.08, C3H6 (propene): 0.78 ± 0.10, C4H8 (trans-butene): 0.69 ± 0.12 (errors are cited at the level of ±1σ). A compilation of the available kinetic data on these reactions has been made in order to propose rate coefficients for each possible channel of the different reactions for astrochemical models.

Graphical abstract: Rate constants and the H atom branching ratio of the reactions of the methylidyne CH(X2Π) radical with C2H2, C2H4, C3H4 (methylacetylene and allene), C3H6 (propene) and C4H8 (trans-butene)

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Article information


Submitted
25 Jul 2008
Accepted
16 Sep 2008
First published
30 Oct 2008

Phys. Chem. Chem. Phys., 2009,11, 655-664
Article type
Paper

Rate constants and the H atom branching ratio of the reactions of the methylidyne CH(X2Π) radical with C2H2, C2H4, C3H4 (methylacetylene and allene), C3H6 (propene) and C4H8 (trans-butene)

J. Loison and A. Bergeat, Phys. Chem. Chem. Phys., 2009, 11, 655
DOI: 10.1039/B812810C

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